When trying to respond to a comment on a chat room, only for someone to comment before you, making your comment lose it's original Context. Depending on the intermediary comment, this can have some humorous results

Dave: Anyone wanna play The new X-Box Game?

Sanders: How about some Dick?
George: ^^ Yeah, I'd want in on that
Sanders: Lol, Gay!
Dave: haha, dude, you got ninjad!

To take something quickly and quitely without anyone noticing. Offen used in the online game WoW when a party member takes an item without the party's consent.

Tim: Dude you gotta see my new phone it's so boss.
*tim reaches in his pocket for his phone*
Tim: What the hell, who ninjad my damn phone?
Mike: oh dude I thought you knew I was looking at it like 5 minutes ago.
Tim: How the??